I propose to carry out a systematic investigation of the neuronal maturation - cortical ontogenesis - and of the fibrillar neuronal structure - cortical organization - of the cerebral cortex of normal and abnormal embryos, fetuses, prematures, newborns and young children. These studies are to be carried out with the rapid Golgi method and with other complementary neurohistologic techniques. The following main objectives will be pursued in this investigation: 1) to establish patterns and time tables of normal events in the course of the sequential maturation and progressive structural organization of the human cerebral cortex; 2) to utilize these observations as control data in the study of the abnormal organization of the human cerebral cortex, including: a) infants with chromosomal aberrations associated with mental retardation; b) infants with severe cerebral anoxia or prolonged use of the respirator; c) infants with congenital malformations involving primarily the cerebral cortex. In addition, I propose to carry out a systematic investigation also with the rapid Golgi method, of the development and structural organization of the mammalian cerebral cortex, in the cat and hamster, to be used in comparative studies with man.